How to Resolve Microsoft Defender’s High CPU Usage Issue on Windows 11

Microsoft Defender is built directly into Windows 11 and provides strong real-time protection without needing a third-party antivirus. But sometimes it can become a little too active, causing unusually high CPU usage. This often happens during background scans, corrupted definition updates, a stuck Antimalware Service Executable process, or when Defender repeatedly scans large folders.

High CPU usage from Microsoft Defender can slow your system down, make apps freeze, or cause your fans to spin faster than usual. The good news is that you can fix this problem with a few simple adjustments.

In this guide, we’ll walk you through all the effective solutions to resolve Microsoft Defender’s high CPU usage issue on Windows 11.

How to Fix Microsoft Defender’s High CPU Usage on Windows 11

Follow the detailed steps below to bring down CPU usage and get your system running smoothly again.

1. Restart Your PC and Wait for Ongoing Scans to Finish

Before diving into advanced fixes, first check whether Defender is simply running a scheduled scan.

1. Press Windows + I to open Settings.
2. Go to Privacy & security.
3. Click Windows Security > Virus & threat protection.
4. If you see a scan in progress, allow it to finish.

If no scan is running, restart your PC. Temporary glitches in the Antimalware Service Executable process often clear after a reboot.

2. Update Microsoft Defender Virus Definitions

Outdated or corrupted security definitions can cause Defender to continuously re-scan files.

1. Open Windows Security.
2. Click Virus & threat protection.
3. Scroll to Virus & threat protection updates.
4. Click Check for updates.

If an update fails repeatedly, try updating using Windows Update instead:

1. Go to Settings > Windows Update.
2. Click Check for updates.

3. Limit Defender’s CPU Usage Using PowerShell

Windows lets you set a CPU threshold for Defender scans.

1. Press Start, type PowerShell, and choose Run as administrator.
2. Run this command to limit CPU usage to 50 percent (you can lower it further if needed):

Set-MpPreference -ScanAvgCPULoadFactor 50

This won’t affect real-time protection but prevents full scans from overloading your processor.

4. Exclude Large Folders or Files from Defender Scans

If you have folders with a huge number of files, such as game directories, virtual machines, or development projects, Defender may repeatedly scan them.

To fix this:

1. Open Windows Security.
2. Go to Virus & threat protection.
3. Scroll down and click Manage settings under Virus & threat protection settings.
4. Scroll to Exclusions and click Add or remove exclusions.
5. Add folders such as:
   • Steam or game library folders
   • Virtual machine directories
   • Developer toolchains
   • Large data folders

This reduces unnecessary scanning and lowers CPU usage significantly.

5. Disable Defender’s Real-Time Protection (Temporary Only)

If CPU usage spikes while performing a specific task, temporarily disable real-time protection.

1. Open Windows Security.
2. Go to Virus & threat protection.
3. Click Manage settings.
4. Turn off Real-time protection.

Reactivate it as soon as you’re done. This is only a short-term step and should not be left off permanently.

6. Turn Off Microsoft Defender’s Automatic Sample Submission

Some users see CPU spikes when Defender tries sending data to Microsoft.

1. Open Windows Security.
2. Go to Virus & threat protection.
3. Click Manage settings.
4. Turn off Automatic sample submission.

This may reduce network activity and CPU strain during scans.

7. Disable Controlled Folder Access (If Constantly Triggering)

Controlled Folder Access sometimes causes repeated checks for app access, spiking CPU usage.

1. Open Windows Security.
2. Choose Ransomware protection.
3. Turn off Controlled Folder Access.

Only disable this if you’re sure no suspicious apps are running.

8. Run SFC and DISM to Repair System Files

System corruption can also make Defender behave strangely.

1. Open Command Prompt (Admin).
2. Run:

sfc /scannow

3. Then run:

DISM /Online /Cleanup-Image /RestoreHealth

4. Restart your PC.

This repairs core Defender components and Windows files.

9. Reset Microsoft Defender Using PowerShell

If Defender’s configuration is corrupted, reset it completely.

1. Open PowerShell (Admin).
2. Run:

Get-AppxPackage Microsoft.SecHealthUI -AllUsers | Reset-AppxPackage

3. Restart your PC.

This reinstalls Defender’s interface and resets protection settings.

10. Perform a Clean Boot to Check for Conflicting Apps

Some background apps (especially third-party antivirus leftovers) conflict with Defender.

1. Press Windows + R, type msconfig, and press Enter.
2. Go to the Services tab.
3. Check Hide all Microsoft services.
4. Click Disable all.
5. Go to Startup > Open Task Manager.
6. Disable all startup apps.
7. Restart your PC.

If CPU usage drops, re-enable items one by one to find the culprit.

11. Install the Latest Windows Updates

Microsoft frequently patches Defender performance issues.

1. Go to Settings > Windows Update.
2. Click Check for updates.
3. Install all pending updates and restart.

Wrapping Up

High CPU usage from Microsoft Defender can slow down your entire system, but in most cases, it’s caused by scans stuck in a loop, outdated definitions, or large directories being scanned repeatedly. By updating Defender, adding exclusions, limiting CPU usage, and repairing system files, you can quickly restore normal performance.

If Defender continues to spike your CPU even after all these fixes, keeping Windows updated and reviewing your startup apps will help prevent the issue from coming back.